1. Field of the Invention
The present invention is related to the measurement methods and measurement apparatuses for non-invasively and quantitatively measuring internal mechanical properties and physical quantities such as a displacement, a strain, a velocity, an acceleration etc. of target objects, substances, materials, living things etc. For instance, the present invention is related to new measurement methods and measurement apparatuses for generating an internal displacement vector distribution, an internal strain tensor distribution, an internal strain rate tensor distribution, an internal acceleration vector distribution etc. by applying a mechanical source such as a compression, a vibration, a radiated force etc. to a target, and generating echo data and imaging data by properly performing beamforming for measuring the physical quantities. Alternatively, the present invention also permits the measurement of spontaneous tissue motion such as of a heart, a lung wall etc., and tissue motion generated by body motion, respiratory, heartbeat, blood pulsation etc. The present invention also permits the measurement of a blood flow vector in a heart and a blood vessel. Such measurements can also be performed simultaneously. The measurement results also permit the measurements of mechanical properties and thermal properties etc. The applications are various.
The typical applications of the present invention in a medical field is to ultrasound (US) diagnosis apparatuses, nuclear magnetic resonance imaging (NMRI) apparatuses, optical diagnosis apparatuses etc. for observing internal tissues (diagnosis of cancerous diseases, infarctions, scleroses, thrombi, hemodynamics, blood oxygen saturations etc.) and radiation therapy apparatuses including a high intensity focus ultrasound (HIFU) apparatus. That is, the present invention permits obtaining a safety and a confidence for such various treatments, and an improvement in treatment effectiveness by tracking tissue displacements in treatment parts etc. as well as for such diagnoses by observing target tissue motions/deformations, hemodynamics and various dynamics. Tissue degenerations can also be monitored for the evaluation of the treatment effectiveness. The applications of the present invention is not limited to these mentioned above. As the non-destructive measurement methods, such evaluations, examinations and diagnoses can also be performed on various objects.
2. Description of a Related Art
For instance, in a medical field, treatment of diseases is performed using a radiation therapy, a high intensity ultrasound radiation, a laser radiation, a radio-frequency (rf) electromagnetic radiation, a microwave electromagnetic radiation, a cryotherapy, a cooling therapy etc. For such treatments, the above-mentioned tissue tracking and monitoring of the treatment effectiveness is proposed to be performed. Alternatively, non-invasive observing of treatment effectiveness is also performed on the use of medicine such as an anti-cancer drug etc. For instance, because the temperature of a disease part changes when such a radiation therapy etc. is performed, the treatment effectiveness can be monitored by non-invasively measuring the generated degeneration (including a temperature change). Otherwise, the evaluation of blood flow in a disease part also permits differential diagnosis on a disease progress etc. Measurement of a displacement, a strain, and changes in displacements and strains etc. generated in a region of interest (ROI) in living tissues such as a disease part and a treatment part by a force applied to the ROI is proposed to be used for diagnosis and observing a treatment effectiveness etc. on the basis of the evaluation of a difference in tissue characteristics (elastic constants etc.) between the part and the surrounding tissues. Such observing is permitted by using the US apparatuses, MRI apparatuses, various optical diagnosis apparatuses including radiation diagnosis apparatuses such as an X-ray diagnosis apparatus, various temperature measurement apparatuses etc., in which features of a wave propagation such as of mechanical waves, electromagnetic waves, thermal waves etc. are used.
It is known that the temperature of the ROI in the target has correlations with elastic constants, visco-elastic constants, delay times and relaxation times determined by elastic constants and visco-elastic constants, density, viscosities etc. Thus, the non-destructive measurement of elastic constants such as shear modulus, Poisson's ratio etc., visco-elastic constants such as visco-shear modulus, visco Poisson's ratio etc., delay times and relaxation times determined by the respective elastic constants and corresponding visco-elastic constants, density, viscosities etc. (e.g., patent documents 2 and 6; non-patent document 20) permits the measurement of a temperature or a temperature distribution in the ROI (e.g., patent document 2). The temperature distribution can also be measured directly by measuring a strain distribution generated by the temperature change. These temperature measurement methods permit the monitoring of various thermal treatments; and an additional calculation of thermal property distributions permit planning of the thermal treatment (e.g., patent document 5).
Alternatively, for instance, US apparatuses used in a medical field transmit ultrasounds from a US transducer to internal target tissues; and receive US echo signals reflected from the internal tissues using the US transducer; and measure a distribution of the tissues etc. on the basis of the conversion of the received echo signals into an observational image etc. The US transducer to be used in the present invention can have various aperture geometries and can employ various type US vibrators. By measuring displacements generated by an arbitrary mechanical source or by calculating distributions of strain tensor or elastic constants from the measured displacement data, differences between diseases such as liver cancers etc. and normal tissues can be observed non-invasively. When using other apparatuses such as NMRI apparatuses, various optical diagnosis apparatuses, various temperature measurement apparatuses, the similar measurement, calculation and imaging can be performed.
Alternatively, measurement and imaging of shear modulus is also performed on the basis of the measurement of shear wave propagation speed, in which the shear wave is generated by using mechanical sources such as a low frequency vibrator and a radiated force (e.g., non-patent document 19). For the measurement of the shear wave propagation speed, the calculation method for measuring a displacement is used (measurement of an instantaneous phase change). An instantaneous phase change between frames can be detected to measure the position where a displacement (strain) wave reaches. In such a case, high measurement accuracy may not be required for the measurement of the instantaneous phase change. This is also for the use of incoherent signals obtained from the coherent echo signals. In contrast, a high measurement accuracy of a tissue displacement is required to achieve a specific and high accuracy measurement of the shear wave. It is valuable to measure the propagation direction of the shear wave with a high accuracy, and if mechanical sources or thermal sources generated using radiated forces can be controlled, the propagation direction of the shear wave can be controlled and the target tissue can be deformed in a proper direction; and anisotropic elastic constant (shear modulus) distributions can be determined. However, a proper method has not been developed yet. However, another method has been developed for the measurement of the shear wave propagation speed particularly useful when using a low frequency vibration, i.e., although generally the measurement becomes difficult when a stationary wave is generated by a reflection phenomenon, it is possible to distinguish the transmission wave and the reflection wave. For a one-dimensional wave propagating in a lateral direction, the method is disclosed in non-patent document 22 etc.; and for a multi-dimensional wave, it is also possible in a similar fashion. However, because the wavelength of the shear wave is long, the spatial resolution achievable for the shear wave propagation speed measurement is low. This is an inherent limitation.
Thus, it is proposed that ultrasounds are transmitted plural times with a temporal interval, and the internal displacement is measured using the change in echo signals obtained at the successive US transmissions. Moreover, it is proposed that internal mechanical quantities such as strains etc. are calculated from the displacements measured at respective positions, and furthermore the tissue characteristics are diagnosed non-invasively. For a three-dimensional (3D), two-dimensional (2D) or one-dimensional (1D) ROI set in the target, the distribution of three, two or one component of a 3D displacement vector generated is measured. The measured displacement data and correspondingly calculated strain data are used to calculate elastic constant distributions etc. in the ROI.
The US transducer has functions of sensors for measuring the displacements and strains generated. Instead of the transducer, other type sensors can also be used such as detectors of a magnetic field, lights, temperature, laser and among others (a contact or non-contact type). For the mechanical source, the US transducer body is used as a compressor or is used as a vibrator by vibrating the body. Other mechanical sources from the US transducer can also be used (i.e., a compressor or a vibrator). Cardiac motion or blood pulsation can also be used as a mechanical source. Otherwise, an internal mechanical source can also be generated by radiating a force. When using a US transducer for radiating the force to generate deformations in the ROI as well as for the sensors for measuring the displacements or strains, other mechanical sources may not be used. For tissue characterization, changes in elastic constants and a temperature due to the thermal treatments and thermal properties as well as the elastic constants can also be used.
However, classical displacement measurement methods yield an only axial displacement measurement by performing 1D signal processing of the US echo signals in the axial (beam) direction (i.e., an axial direction is set in the direction of a beam direction) under the assumption that the target displacement directs in the axial direction. Hereafter, US echo signals include raw signals, quadrature- or envelope-detected signals, analytic signals etc. Because a practically generated displacement vector has displacement components with directions orthogonal to the axial (beam) direction, when using such classical methods, the measured axial displacement has a low accuracy (non-patent document 1). Furthermore, it is also impossible to measure the displacement components with directions orthogonal to the axial direction. For instance, it is difficult to accurately measure a blood flow (vector) in a heart and a blood vessel running parallel to the body surface and a tissue motion/deformation for tissues of which deformations cannot be controlled externally or the deformations are generated by cardiac motion or blood pulsation such as deeply situated tissues (e.g., liver).
In contrast, the present inventor proposes measurement methods of the displacement vector, i.e., methods using a multidimensional (i.e., 3D or 2D) cross-correlation or a phase gradient of a multidimensional cross-spectrum of echo signals (non-patent documents 1, 2 etc., i.e., one of high accuracy block matching methods together with the cross-correlation method). For the displacement vector measurement, the present inventor also proposes the multidimensional autocorrelation method and multidimensional Doppler method using multidimensional analytic signals etc. (patent documents 2, 4; non-patent document 3 etc.). From the viewpoints of a measurement accuracy and a calculation time required for the measurement purposes, these methods can be properly used, respectively. Otherwise, proper combinations of the methods can also be used.
In addition to the multidimensional measurement methods, the multidimensional phase matching method that the present inventor previously developed is effective (non-patent documents 1 to 5). The multidimensional phase matching prevents the measurement from phase aliasing due to a large displacement in the beam direction, and increases the measurement accuracy in all displacement vector components by increasing a correlation or a coherency between the pre- and post-deformed echo signals obtained from target tissues by performing a coarse matching of the echo signals in a multidimensional space (i.e., including lateral and/or elevational direction) using the coarse displacement estimates obtained using a multidimensional method such as the multidimensional cross-correlation method or multidimensional cross-spectrum phase gradient method before performing fine measurement of the target displacement vector with respect to the same echo signals using the multidimensional cross-spectrum phase gradient method, multidimensional autocorrelation method or multidimensional autocorrelation method (non-patent documents 1 to 3). Otherwise, although the measurement accuracy decreases, only the axial displacement is measured using low dimensional signal processing such as 1D signal processing instead of the multidimensional methods after the coarse measurement (non-patent documents 4, 5 etc.). For the coarse measurement, 1D signal processing etc. can also be performed in the respective directions.
When using the phase gradient of cross-spectrum, particularly for the coarse measurement, echo signals thinned out can be processed, i.e., with a coarse sampling interval (non-patent document 3). Although the phase matching can be performed in a frequency domain using phase rotation with complex exponential multiplication (non-patent documents 1 to 5), because the method requires a long calculation time, echo data in a searching region or a target local region can also be spatially shifted in a space (non-patent documents 1 to 5). When calculating the coarse displacement components from the phase gradient of cross-spectrum, because the original calculation results are analogue, the results are approximated by multiplications of integers and sampling intervals to permit the spatial shifting of echo signals. When using the cross-correlation method, calculation results of displacements are originally the multiplications of integers and sampling intervals. Because the cross-spectrum phase gradient method requires fewer calculations to achieve the measurement than the cross-correlation method, the cross-spectrum phase gradient method is more proper for real-time measurement.
For instance, by using these measurement methods, a displacement vector and an axial displacement can also be measured when uncontrollable mechanical sources exist (for living tissues, for instance, hear motion, respiratory, blood vessel pulsation, body motion etc.; lung, air, blood vessel, blood etc. are included in the ROI) as well as when using a compressor or a vibrator (US transducer may be used), a radiated force (US transducer may generate the force), etc. Thus, the multidimensional phase matching prevents the measurement from acquiring improper echo data. Similarly to the classical 1D measurement methods, these multidimensional displacement vector measurement methods also achieve real-time display of the measurement results through high speed calculation.
However, if displacements with the directions orthogonal to the axial (beam) direction remain after the phase matching, the measurement accuracy of the displacement vector and axial displacement decreases. That is, the measurement accuracy depends on the degree of the fineness of phase matching. Particularly when performing displacement vector measurement using conventional diagnosis apparatuses, because there are no carrier frequencies in the lateral and elevational directions; and lateral and elevational bandwidths are smaller than axial bandwidth, correspondingly measurement accuracies and spatial resolutions of the lateral and elevational displacement components decrease. Thus, being dependent on a measurement accuracy of lateral and elevational displacements, the measurement accuracy of the multidimensional displacement vector and strain tensor becomes low.
For such measurements, the present inventor has already realized a high accuracy measurement using generation method of echo data with lateral and elevational carrier frequencies together with above-mentioned displacement vector measurement methods. The accuracy of not only lateral and elevational displacement components but also an axial displacement component increased. It is a lateral modulation (LM) (for instance, non-patent documents 3, 6, 7 etc.). Jensen et al. determined an apodization function using the Fraunhofer approximation to generate a desired point spread function (PSF) (non-patent documents 8 and 9); the present inventor determined apodization functions on the basis of an optimization theory (patent document 3; non-patent documents 10, 11 etc.). The present inventor also determines the apodization function using the knowledge about the ultrasound propagation properties (for instance, non-patent documents 6, 7, 12 etc.). The present inventor also confirmed that power functions are proper functions for the apodization. The above-mentioned LM which the present inventor developed can also be used for echo imaging, in which almost the same high frequency can be obtained for the lateral direction as that for the axial direction. Thus, it is expected that LM beamforming becomes one of operation modes of general US diagnosis apparatuses.
For the transmission and reception beamforming, monostatic or multistatic synthesizing apertures can be performed for respective sets of received echo data. Simultaneously plural beams spatially crossed can be transmitted and received; simultaneously plural plane waves spatially crossed can be transmitted in order to superpose echo data received from a wide region (a high speed beamforming); plural crossed beams generated using plural physical apertures can be superposed; plural crossed beams obtained at different times can be superposed. Thus, the present inventor have developed various LM methods (patent documents 6 and 7; non-patent documents 3, 6, 7 etc.). Although LM can also be performed without consideration about the apodization (i.e., beam shape), performing above-mentioned optimized apodization permits a wideband echo data generation; US LM imaging can be achieved with a high spatial resolution and furthermore the displacement vector measurement can also be achieved with a considerably high accuracy.
When performing the LM regardless performing such apodization or not, a 3D echo data frame used for 3D displacement vector measurement can be obtained by superposing plural beams, ones steered in four or three directions (i.e., crossed beams); a 2D echo data frame used for 2D displacement vector measurement can be obtained by superposing two-directional steered beams (i.e., crossed beams) (non-patent document 3). Also in the present invention, the respective 3D or 2D echo data frames successively generated are dealt with as temporal series of an echo data frame that exhibits target tissue distribution at a temporal phase approximately. The inverse of the time between the frames is called as a frame rate. In order to deal with such respective 3D or 2D echo data frames at different temporal phases, because the tissue displacement exists between the echo data frames, it is desirable to generate the echo data frames from plural or single echo data received as in a short time as possible. Hereafter, in the present invention, “a temporal phase” is used in this sense.
For the tissue displacement vector measurement, the multidimensional cross-spectrum phase gradient method (non-patent documents 1 and 2), the multidimensional autocorrelation method (patent documents 2 and 4; non-patent document 3), the multidimensional Doppler method (patent documents 2 and 4; non-patent document 3) and the multidimensional cross-correlation method (non-patent documents 1 and 2) etc. can be used. All these measurement methods permit measurement of all displacement vector component distributions simultaneously for a displacement vector distribution generated between echo data frames at plural temporal phases. Because these measurement methods perform all processing such as moving-average processing etc. under the assumption that displacement components in plural directions exist, a considerably high accuracy measurement is achieved (non-patent document 13). On the same LM echo data frame obtained, the demodulation (patent document 1) can be implemented to yield echo data frames with carrier frequencies in the respective directions. In such a case, one-directional displacement measurement methods can be used to yield displacement vector measurement. In order to perform analogue demodulation (non-patent documents 14 and 15), plural echo data frames must be generated by transmission and reception of ultrasounds. However, when using echo data correspondingly obtained for beams physically transmitted at different times, the displacements generated between the transmissions lead to measurement errors. Also rapid motion rather than beam scanning decreases the measurement accuracy. In contrast, the demodulation which the present inventor developed (patent document 1) yields accurate measurements, because the demodulation is achieved through generation of only one echo data frame at a temporal phase and digital signal processing. However, a common problem exists for the analogue and digital methods. That is, because there exits displacements in the directions orthogonal to the direction with a carrier frequency, even if multidimensional moving-average is performed to mitigate the decrease in a measurement accuracy, an achievable accuracy is lower than that achieved using the multidimensional displacement vector measurement methods (non-patent document 13).
In view of a beamforming, these LMs require more beams than conventional beamforming to generate one echo data frame (above-mentioned 3D or 2D echo data). In addition, signal processing for acquiring echo data and generating echo data becomes more (i.e., apodization, switching, delay processing, phase matching, summation processing etc.). These lead to more time consumption for beamforming and a low frame rate. When LM is performed by synthetic aperture (SA) processing, according to a feature of SA, dynamic focusing can be performed at transmission as well as at reception. However, when the transmission powers from respective US vibrators (elements) are small, the signal-to-noise ratio of echo signal to be obtained becomes small. Moreover, a larger physical aperture is required than that required for conventional beamforming. Then, when obstacles such as bones etc. exist in the superficial tissues, deeply situated tissues cannot be dealt with. Moreover, a field of vision becomes small in the lateral and elevational directions as well.
Alternatively, for a high accuracy measurement, plural beams with different directions are realized similarly to the above-mentioned LMs, and however, a displacement vector can also be synthesized using axial displacement measurements obtained with a high accuracy from the echo data with the respective directional beams (i.e., non-superposed echo data). In the present invention, the measurement method is referred to as the multidirectional beamforming method (non-patent document 3). For the respective axial displacement measurement, not the one-directional displacement measurement methods but the above-mentioned multidimensional displacement vector measurement methods should be used similarly to in the LM cases (non-patent document 3). That is, the existence of displacements with the directions orthogonal to the beam direction should be considered. However, similarly to in the LM cases, the frame rate decreases. When using echo data correspondingly obtained for beams physically transmitted at different times, the displacements generated between the transmissions also lead to a measurement error. Also rapid motion rather than beam scanning decreases the measurement accuracy.
Then, the present inventor developed a new beamforming method that allows decreasing the measurement errors caused by the tissue displacements generated during the generation of an echo data frame by decreasing the time required for performing a beamforming. Consequently, real-time and high accuracy measurements of a displacement vector and a one-directional displacement were realized (patent document 1 and non-patent document 16 etc.).
A displacement measurement method exposed in the patent document 1 comprises the steps of:
(a) transmitting ultrasounds to an object using at least one ultrasound vibrator and yielding ultrasound echo data frames with respect to the object in an arbitrary direction using an ultrasound beam steered electrically and/or mechanically with a single steering angle over one of a three-dimensional orthogonal coordinate system having three axes substantially in a depth direction, a lateral direction orthogonal to the depth direction, and an elevational direction orthogonal to the depth direction and the lateral direction, and a two-dimensional orthogonal coordinate system having two axes substantially in a depth direction and a lateral direction orthogonal to the depth direction; and
(b) calculating a displacement vector distribution by implementing a predetermined block matching on the ultrasound echo data frames yielded at more than two temporal phases.
For the transmission and reception beamforming, the classical monostatic or multistatic synthetic aperture (SA) method can be used; the scanning with a physically generated, steered beam can also be performed; the reception beamforming can also be performed on echo data obtained with respect to one or plural laterally wide wave transmissions such as non-steered (frontal with respect to an physical effective aperture) or steered plane wave transmissions on a Cartesian coordinate system at the same time or at the same temporal phase (i.e., high speed beamforming: on an arbitrary coordinate system, the transmission of one or plural laterally wide waves are performed at the same time or at the same temporal phase); and among others. Mechanical scanning solo or together with electrical scanning can be performed. That is, a 3D or 2D US echo data frame can be generated using an ultrasound beam electrically and/or mechanically steered with a single steering angle over the object.
A displacement measurement apparatus exposed in the patent document 1 comprises:
a transducer comprising at least one ultrasound vibrator configured to transmit ultrasounds to an object in accordance with at least one drive signal, and to detect ultrasound echo signals generated in the object to output echo signals;
a driving and processing unit configured to supply the at least one drive signal to the vibrator, and processing the echo signals outputted from the vibrator;
a control unit configured to control respective units to yield ultrasound echo data frames with respect to the object in an arbitrary direction using an ultrasound beam steered electrically and/or mechanically with a single steering angle over one of a three-dimensional orthogonal coordinate system having three axes substantially in a depth direction, a lateral direction orthogonal to the depth direction, and an elevational direction orthogonal to the depth direction and the lateral direction, and a two-dimensional orthogonal coordinate system having two axes substantially in a depth direction and a lateral direction orthogonal to the depth direction; and
a data processing unit configured to calculate a displacement vector distribution by implementing a predetermined block matching on the ultrasound echo data frames yielded at more than two temporal phases.
For the transmission and reception beamforming, the classical monostatic or multistatic synthetic aperture (SA) method can be used; the scanning with a physically generated, steered beam can also be performed; the reception beamforming can also be performed on echo data obtained with respect to one or plural laterally wide wave transmissions such as non-steered (frontal) or steered plane wave transmissions on a Cartesian coordinate system at the same time or at the same temporal phase (i.e., high speed beamforming: on an arbitrary coordinate system, the transmission of one or plural laterally wide waves are performed at the same time or at the same temporal phase); and among others. Mechanical scanning solo or together with electrical scanning can be performed. That is, a 3D or 2D US echo data frame can be generated using an ultrasound beam electrically and/or mechanically steered with a single steering angle over the object.
The beamforming method exposed in the patent document 1 performs apodization, switching, delay, phase matching, summation processing, and occasionally mechanical scanning, and on the basis of such processing, the beamforming method performs beam steering by transmitting a steered beam with a steering angle in a 3D or 2D ROI, or a 1D ROI in a lateral direction primarily or in a depth direction in the object and receiving a steered beam with the same steered beam with respect to echo signals generated in the object. If necessary, the beamforming method performs scanning with the steered beam with respect to the object to obtain a 3D or 2D echo data frame. On the basis of the phase difference between the steered beams or the echo data frames with the same steering angle obtained at different temporal phases using the beamforming method, the combinational use of the above-mentioned displacement vector measurement method or the above-mentioned one-directional displacement measurement method permits measurement of a local displacement vector or a local one-directional displacement in a lateral direction primarily or in a depth direction, or a distribution of the local displacements. For a displacement vector measurement, the present inventor also developed the spectra frequency division method that divides spectra in a frequency domain and yields plural Doppler equations for the multidimensional autocorrelation method or multidimensional Doppler method from the respective divided spectra (i.e., multidimensional analytic signals obtained from the divided spectra).
For the transmission and reception beamforming, the classical monostatic or multistatic synthetic aperture (SA) method can be used; the scanning with a physically generated, steered beam can also be performed; the reception beamforming can also be performed on echo data obtained with respect to one or plural laterally wide wave transmissions such as non-steered (frontal) or steered plane wave transmissions on a Cartesian coordinate system at the same time or at the same temporal phase (i.e., high speed beamforming: on an arbitrary coordinate system, the transmission of one or plural laterally wide waves are performed at the same time or at the same temporal phase); and among others. Mechanical scanning solo or together with electrical scanning can be performed. That is, a 3D or 2D US echo data frame can be generated using an ultrasound beam electrically and/or mechanically steered with a single steering angle over the object. In the present invention, the beamforming is referred to as a steering angle (ASTA) beamforming method.
As disclosed in the non-patent document 6, the ASTA beamforming method does not require the generation of plural beams, and the possibly decreases the measurement errors or affections caused by the tissue displacements during the generation of one echo data frame by performing beam scanning. Because the ASTA beamforming does not always yield the best measurement and imaging, other beamforming such as the LM beamforming (patent document 1: virtual source or virtual receiver can also be used), non-steered (frontal) beamforming with respect to the physical aperture and among others that are permitted by the same hardware components that permits the ASTA beamforming can also be selected together with displacement measurement methods. The US diagnosis apparatus disclosed in the patent document 1 is equipped with the function for selecting their beamforming methods and displacement measurement methods. Moreover, a transmission can also be performed with respect to an arbitrary direction over a laterally wide ROI at the same time or at the same temporal phase. Synthetic aperture can also be performed. When using a 1D or 2D arrayed-type transducer, independent various beamforming can also be performed simultaneously at separate positions such that the generated beams do not overlap. Other virtual sources can also be used (see for instance, patent document 1) and for a high speed imaging, other beamforming methods can also be used.
According to the patent document 1, on the basis of the scanning with the ASTA beamforming (i.e., steering with a steering angle) and properly combinational use of the above-mentioned displacement measurement methods allows providing a new real time, high accuracy displacement vector measurement or a new real-time, high accuracy one-directional displacement measurement in a lateral direction primarily and in a depth direction, a new displacement measurement apparatus and a new US diagnosis apparatus.